1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a germanium (Ge) phototransistor and associated fabrication process that capitalizes on the floating body effect of a device insulated from an underlying substrate.
2. Description of the Related Art
FIG. 1 is a Cross-Sectional Transmission Electron Microscopy (XTEM) image of an interface between Ge and Si3N4. The Ge film has been regrown by liquid phase epitaxy. In a co-pending application entitled METHOD OF EPITAXIAL GROWTH OF GERMANIUM PHOTODETECTOR FOR CMOS IMAGER, Lee et al., Ser. No. 11/069,424, filed Feb. 28, 2005, a method for growing single crystalline Ge film by liquid phase epitaxy is presented, along with a means of fabricating a PIN photo detector for infrared photon detection. However, it is noted that the interface between Ge single crystal and the bottom dielectric layer (Si3N4) is not perfect, as shown in the TEM image. This interface may potentially cause leakage current in the diode. This interface is likely the result of the Ge PIN diode using the entire Ge film, so that the bottom interface deteriorates the electrical performance.
It would be advantageous if an improved interface could be created between the epitaxial layer of a Ge active device and the underlying substrate insulator.
It would be advantage if a Ge device could be fabricated so as to minimize the effect of the substrate interface.
It would be advantageous if the epitaxial layer of a Ge active device could be more effectively insulated from an underlying Si substrate.